In recent years, a use application as a medium for data archive for preserving important data in the long term has attracted attention as a use application of an optical disc such as a Blu-ray (registered trademark) Disc (hereinafter referred to as a BD). The higher-linear density promotion is required for the optical disc for data archive in order to enable the more data to be preserved.
The recording of the data in the optical disc is carried out by forming a mark and a space in a recording layer. The intensity of a laser beam is modulated on the basis of a recording pattern, and the recording layer is irradiated with a recording pulse, thereby forming the mark.
On the other hand, the laser beam is applied to the recording layer, and a regenerative signal as a change in light quantity of return light generated from the optical characteristics such as a difference in reflectivity between the mark and the space is obtained, thereby reproducing the recorded data. Signal processing is executed for the regenerative signal, thereby reproducing the recorded data.
At the time of recording of the data, for reducing the error in the regenerative signal, the recording compensation for adjusting edge positions of a start edge and an end edge of the mark. The recording compensation is especially required in the case where an optical disc in which a mark length and a space length are much smaller than an optical spot size, that is, an optical disc for a high-linear density is used.
In the case where the length of the space is short, the heat when the mark is formed is not sufficiently reduced in the space portion, which exerts an influence on the temperature of the edge of the start edge in the rear-side mark. Contrary to this, the heat when the edge of the start edge in the rear-side mark is formed exerts an influence on the cooling of the heat at the edge of the end edge of the front-side mark. Such a thermal interference causes the position shift in the recorded mark. In the case where the optical disc in which the mark position is shifted is subjected to the reproduction, the regenerative signal is influenced, so that the data cannot be properly reproduced.
The recording compensation is processing for finely adjusting the pulse shape of the laser beam to compensate (shift) the edge portion of the mark which is fluctuated by the thermal interference to the proper position. In the BDXL (registered trademark) standards as the extended standards of the BD standards, an L-SEAT method is adopted as a method for estimation and adjustment of the edge shift. The L-SEAT method is disclosed in PTL 1.